U.S. patent application number 16/744269 was filed with the patent office on 2020-05-14 for method of determining a position of a feature.
This patent application is currently assigned to ASML NETHERLANDS B.V.. The applicant listed for this patent is ASML NETHERLANDS B.V.. Invention is credited to Hakki Ergun Cekli, Chi-Hsiang Fan, Ralph Timotheus HUIJGEN, Masashi Ishibashi, Marc Jurian Kea, Liping Ren, Maurits Van Der Schaar, Marcel Theodorus Maria Van Kessel, Youping Zhang.
Application Number | 20200150547 16/744269 |
Document ID | / |
Family ID | 57609779 |
Filed Date | 2020-05-14 |
![](/patent/app/20200150547/US20200150547A1-20200514-D00000.png)
![](/patent/app/20200150547/US20200150547A1-20200514-D00001.png)
![](/patent/app/20200150547/US20200150547A1-20200514-D00002.png)
![](/patent/app/20200150547/US20200150547A1-20200514-D00003.png)
![](/patent/app/20200150547/US20200150547A1-20200514-D00004.png)
![](/patent/app/20200150547/US20200150547A1-20200514-M00001.png)
United States Patent
Application |
20200150547 |
Kind Code |
A1 |
HUIJGEN; Ralph Timotheus ;
et al. |
May 14, 2020 |
METHOD OF DETERMINING A POSITION OF A FEATURE
Abstract
A method, system and program for determining a position of a
feature referenced to a substrate. The method includes measuring a
position of the feature, receiving an intended placement of the
feature and determining an estimate of a placement error based on
knowledge of a relative position of a first reference feature
referenced to a first layer on a substrate with respect to a second
reference feature referenced to a second layer on a substrate. The
updated position may be used to position the layer of the substrate
having the feature, or another layer of the substrate, or another
layer of another substrate.
Inventors: |
HUIJGEN; Ralph Timotheus;
(Hillsboro, CA) ; Kea; Marc Jurian; (Morgan Hill,
CA) ; Van Kessel; Marcel Theodorus Maria;
(Maastricht, NL) ; Ishibashi; Masashi; (Eindhoven,
NL) ; Fan; Chi-Hsiang; (San Jose, CA) ; Cekli;
Hakki Ergun; (Eindhoven, NL) ; Zhang; Youping;
(Cupertino, CA) ; Van Der Schaar; Maurits;
(Eindhoven, NL) ; Ren; Liping; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASML NETHERLANDS B.V. |
Veldhoven |
|
NL |
|
|
Assignee: |
ASML NETHERLANDS B.V.
Veldhoven
NL
|
Family ID: |
57609779 |
Appl. No.: |
16/744269 |
Filed: |
January 16, 2020 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
16465161 |
May 30, 2019 |
10578980 |
|
|
PCT/EP2017/080190 |
Nov 23, 2017 |
|
|
|
16744269 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 21/956 20130101;
G03F 9/7046 20130101; G03F 9/7092 20130101; G03F 7/70775 20130101;
G03F 7/705 20130101; G03F 7/70633 20130101; G03F 7/70625 20130101;
G03F 7/70691 20130101 |
International
Class: |
G03F 7/20 20060101
G03F007/20; G03F 9/00 20060101 G03F009/00; G01N 21/956 20060101
G01N021/956 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2016 |
EP |
16206732.6 |
Claims
1.-15. (canceled)
16. A method comprising: determining a relative shift of a first
mark with respect to a second mark, wherein a substrate has the
first mark and the second mark on one layer of the substrate and
the first mark is different from the second mark; and controlling,
based on the determined relative shift, positioning of the one
layer of the substrate, a further layer of the substrate or a layer
of a further substrate.
17. The method of claim 16, wherein the first mark and the second
mark have different sensitivities to an aberration in a projection
system, the projection system used to expose the first mark and the
second mark on the substrate.
18. The method of claim 16, further comprising determining a
projection system induced error using the determined relative shift
and the controlling positioning of the one layer of the substrate,
a further layer of the substrate or a layer of a further substrate
uses the determined projection system induced error.
19. The method of claim 16, further comprising measuring a position
of the first mark and the second mark and calculating the distance
between the first mark and the second mark, wherein the relative
shift is determined using the calculated distance between the first
mark and the second mark and an expected distance between the first
mark and the second mark.
20. The method of claim 16, wherein the relative shift is
determined using a diffraction based measurement.
21. The method of claim 16, wherein the determined relative shift
is used in a feedback loop to control positioning of a layer of a
further substrate and/or in a feedforward loop to control
positioning of a further layer of the same substrate.
22. The method of claim 16, wherein the first mark is an alignment
mark or an overlay mark, and wherein the second mark is a product
feature or a feature having a similar response to a projection
system induced error as a product feature.
23. The method of claim 16, wherein the layer comprising the first
mark comprises at least five to ten first marks and the layer
comprising the second mark comprises the same number of second
marks.
24. The method of claim 16, wherein the first mark and the second
mark overlap.
25. The method of claim 16, wherein the first mark has multiple
first portions and the second mark has multiple second
portions.
26. A computer program product comprising a non-transitory
computer-readable medium having instructions therein, the
instruction, upon execution by a computer system, configured to
cause the computer system to at least perform the method of claim
16.
27. A method comprising: determining a position of a first mark,
wherein a substrate has the first mark on a first layer of the
substrate and a second mark on a second layer of the substrate and
the second mark comprises at least one first portion and at least
one second portion; determining a relative shift of the at least
one first portion with respect to the at least one second portion;
and controlling, based on the determined position and the
determined relative shift, positioning of the first layer or a
further layer of the substrate or any layer on a further
substrate.
28. The method of claim 27, wherein the at least one first portion
and the at least one second portion have different sensitivities to
an aberration in a projection system, the projection system used to
expose the second mark.
29. The method of claim 27, wherein the relative shift is
determined by measuring of a position of the at least one first
portion and a position of the at least one second portion and/or
using a diffraction based measurement.
30. The method of claim 27, wherein the first mark has multiple
first portions and the second mark has multiple second
portions.
31. The method of claim 30, wherein the first portions and the
second portions are interlaced.
32. The method of claim 30, wherein the first portions are
substantially consistent in shape and pitch, and the second
portions are substantially consistent in shape and pitch.
33. The method of claim 27, wherein a first portion comprises fewer
elements than a second portion.
34. The method of claim 27, wherein a first portion comprises only
a single element.
35. The method of claim 27, wherein a single element of a first
portion is larger than a single element of a second portion.
36. The method of claim 27, wherein at least one second portion of
the at least one second portion comprises a plurality of
elements.
37. The method of claim 36, wherein a pitch between a plurality of
second portions is larger than a pitch between the plurality of
elements of the at least one second portion.
38. The method of claim 36, wherein a single element of a first
portion corresponds in size to the plurality of elements making up
at least one second portion.
39. The method of claim 27, wherein the determined position and the
relative shift are used to determine a projection system induced
error and the projection system induced error is used to control
positioning of the first layer or a further layer of the substrate
or any layer on a further substrate.
40. The method of claim 39, wherein the determined projection
system induced error is used in a feedback loop to control
positioning of a layer of a further substrate and/or in a
feedforward loop to control positioning of a further layer of the
same substrate.
41. A computer program product comprising a non-transitory
computer-readable medium having instructions therein, the
instruction, upon execution by a computer system, configured to
cause the computer system to at least perform the method of claim
27.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/465,161, filed May 30, 2019, which is the
U.S. national phase entry of PCT patent application no.
PCT/EP2017/080190, filed Nov. 23, 2017, which claims the benefit of
priority of European patent application no. 16206732.6, filed Dec.
23, 2016, each of the foregoing applications is incorporated herein
in its entirety by reference.
FIELD
[0002] The present description relates to a method, system and
program for determining a position of a feature referenced to a
substrate and methods, system and programs for controlling
positioning of a substrate.
BACKGROUND
[0003] A lithographic apparatus is a machine that applies a desired
pattern onto a substrate, usually onto a target portion of the
substrate. A lithographic apparatus can be used, for example, in
the manufacture of integrated circuits (ICs). In that instance, a
patterning device, which is alternatively referred to as a mask or
a reticle, may be used to generate a circuit pattern to be formed
on an individual layer of the IC. This pattern can be transferred
onto a target portion (e.g., including part of, one, or several
dies) on a substrate (e.g., a silicon wafer). Transfer of the
pattern is typically via imaging onto a layer of
radiation-sensitive material (resist) provided on the substrate. In
general, a single substrate will contain a network of adjacent
target portions that are successively patterned. These target
portions are commonly referred to as "fields".
[0004] In lithographic processes, it is desirable to frequently
measure the structures created forming a circuit pattern, e.g., for
process control and verification. Various tools for making such
measurements are known, including scanning electron microscopes,
which are often used to measure critical dimension (CD), and
specialized tools to measure overlay, which is the accuracy of
alignment of two layers in an at least partially patterned
substrate.
[0005] Various techniques can be used to measure performance of the
lithographic process. This in turn allows sophisticated process
corrections to be included in the control of the operations
performed by the lithographic apparatus. For example, a feedback
system as described below is generally known for making corrections
to the positioning of the substrates in the system by measuring the
positioning error between two different layers of the substrate.
The positioning error between the two different layers of the
substrate is called the overlay error.
[0006] Before exposure of a substrate, the substrate is aligned.
The goal of the alignment is to determine, for each substrate, the
field centres and local distortions, to limit overlay error between
layers of the substrate. This is accomplished by measuring
alignment marks that are printed on at least one layer of the
substrate. The difference between the expected and measured
location of the alignment marks is used as the input for the
alignment model. The alignment model (which may be based on a
linear or higher order alignment) gives an output comprising
parameters used for optimizing the position of the substrate during
subsequent exposure of the substrate.
[0007] To further control the errors in positioning, a feedback
system is used often called an automated process control (APC)
system. The APC system measures the overlay error for a number of
substrates and determines corrections required to reduce the
overlay error. These corrections are then used as input for future
exposures. The APC system typically includes high-order corrections
per exposure. The APC system is intended to correct slowly changing
overlay errors as overlay error measurement is done only on a per
lot basis. The APC system is intended to correct for varying
effects from layer to layer and from lot to lot.
[0008] These corrections typically correct for deformation of the
substrate due to, for example, process variations, clamping
variations and/or temperature variations. These effects can vary
significantly per substrate and the process of using the lot based
APC control for the overlay error still results in undesirable
errors in the positioning of the substrate.
[0009] Furthermore, variations can be introduced due to temperature
changes in a projection system of lithographic apparatus. The
temperature changes can affect the illumination conditions which
affects different marks in different ways. Although the APC control
attempts to account for these variations, there are still
undesirable errors due to temperature changes across the projection
system.
SUMMARY
[0010] An embodiment of the present invention has the aim of
improving determining the position of a feature referenced to a
substrate and improving controlling positioning of a substrate.
[0011] According to an aspect of the invention, there is provided a
method for determining a position of a feature referenced to a
substrate, the method comprises: obtaining a measured position of
the feature, wherein the feature is configured to enable
positioning of the substrate; receiving an intended placement of
the feature; determining an estimate of a placement error, wherein
the placement error is the difference between the intended
placement and an actual placement of the feature, based on
knowledge of a relative position of a first reference feature
referenced to a first layer with respect to a second reference
feature referenced to a second layer, wherein the first layer and
the second layer are on a substrate; and determining an updated
position for the feature using the estimate of the placement error
and the measured position of the feature.
[0012] According to another aspect of the invention, there is
provided a system comprising a processor configured to determine a
position of a feature referenced to a substrate, the processor
configured to: measure a position of the feature, wherein the
feature is configured to enable positioning of the substrate;
receive an intended placement of the feature; determine an estimate
of a placement error, wherein the placement error is the difference
between the intended placement and an actual placement of the
feature, based on knowledge of a relative position of a first
reference feature referenced to a first layer with respect to a
second reference feature referenced to a second layer, wherein the
first layer and the second layer are on a substrate; and determine
an updated position for the feature using the estimate of the
placement error and the measured position of the feature.
[0013] According to another aspect of the invention, there is
provided a program for controlling determining a position of a
feature referenced to a substrate, the program comprises
instructions for carrying out the steps of: measuring a position of
the feature, wherein the feature is configured to enable
positioning of the substrate; receiving an intended placement of
the feature; determining an estimate of a placement error, wherein
the placement error is the difference between the intended
placement and an actual placement of the feature, based on
knowledge of a relative position of a first reference feature
referenced to a first layer with respect to a second reference
feature referenced to a second layer, wherein the first layer and
the second layer are on a substrate; and determining an updated
position for the feature using the estimate of the placement error
and the measured position of the feature.
[0014] According to another aspect of the invention, there is
provided a method for controlling positioning of a substrate,
comprising: providing a substrate with a first mark and a second
mark on one layer of the substrate, wherein the first mark is
different from the second mark; determining a relative shift of the
first mark with respect to the second mark; and controlling
positioning of the one layer of the substrate, a further layer of
the substrate or a layer of a further substrate based on the
determined relative shift.
[0015] According to another aspect of the invention, there is
provided a method for controlling positioning of a substrate,
comprising: providing a substrate with a first mark on a first
layer and a second mark on a second layer of the substrate, the
second mark comprising at least one first portion and at least one
second portion; determining the position of the first mark;
determining a relative shift of the at least one first portion with
respect to the at least one second portion; and controlling
positioning of the first layer or a further layer of the substrate
or any layer on a further substrate based on the determined
position and the determined relative shift. According to another
aspect of the invention, there is provided a system comprising a
processor configured to control positioning of a substrate, the
processor being configured to: determine a relative shift of a
first mark with respect to a second mark, wherein the first mark
and the second mark are on one layer of a substrate, wherein the
first mark is different from the second mark; and control
positioning of a further layer of the substrate or a layer of a
further substrate using the determined relative shift.
[0016] According to another aspect of the invention, there is
provided a program for controlling positioning of a substrate, the
program comprising instructions for carrying out the steps of:
determining a relative shift of a first mark with respect to a
second mark, wherein the first mark and the second mark are on one
layer of a substrate, wherein the first mark is different from the
second mark; and controlling positioning of a further layer of the
substrate or a layer of a further substrate using the determined
relative shift.
[0017] According to another aspect of the invention, there is
provided a system comprising a processor configured to control
positioning of a substrate, the processor being configured to:
provide a substrate with a first mark on a first layer and a second
mark on a second layer of the substrate, the second mark comprising
at least one first portion and at least one second portion;
determine the position of the first mark; determine a relative
shift of the at least one first portion with respect to the at
least one second portion; and use the determined position and the
determined relative shift to control positioning of the first layer
or a further layer of the substrate or any layer on a further
substrate.
[0018] According to another aspect of the invention, there is
provided a program for controlling positioning of a substrate, the
program comprising instructions for carrying out the steps of:
providing a substrate with a first mark on a first layer and a
second mark on a second layer of the substrate, the second mark
comprising at least one first portion and at least one second
portion; determining the position of the first mark; determining a
relative shift of the at least one first portion with respect to
the at least one second portion; and using the determined position
and the determined relative shift to control positioning of the
first layer or a further layer of the substrate or any layer on a
further substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying schematic
drawings in which:
[0020] FIG. 1 depicts a lithographic apparatus together with other
apparatuses forming a production facility for semiconductor
devices, as an example of a system in which an embodiment of the
invention may be used;
[0021] FIG. 2 is a flowchart of a method of determining and using
an updated position of a feature of a substrate;
[0022] FIG. 3 is a flowchart of a method of determining and using
an updated position of a feature of a substrate;
[0023] FIG. 4A illustrates the position of a first mark and a
second mark when there is no projection system induced error and
FIG. 4B illustrates the position of the first mark and the second
mark when a projection system induced error has caused a shift of
the second mark;
[0024] FIG. 5 illustrates an example of the first and second mark;
and
[0025] FIG. 6 is a flowchart of a method of controlling positioning
of a substrate.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0026] Before describing embodiments of the invention in detail, it
is instructive to present an example environment in which
embodiments of the present invention may be implemented. An
embodiment of the invention can be applied, for example, in
controlling a process step in a lithographic manufacturing process.
An embodiment of the invention can be applied for example to
control a lithographic apparatus, when applying patterns at
locations across one or more substrates. A lithographic process for
the manufacture of semiconductor devices will be described to
provide an exemplary context in which the method can be used. The
principles of the present disclosure can be applied in other
processes without limitation.
[0027] FIG. 1 shows a lithographic apparatus LA at 100 as part of
an industrial facility implementing a high-volume, lithographic
manufacturing process. In the present example, the manufacturing
process is adapted for the manufacture of semiconductor products
(integrated circuits) on substrates such as semiconductor wafers.
The skilled person will appreciate that a wide variety of products
can be manufactured by processing different types of substrates in
variants of this process. The production of semiconductor products
is used purely as an example which has great commercial
significance today.
[0028] Within the lithographic apparatus (or "litho tool" 100 for
short), a measurement station MEA is shown at 102 and an exposure
station EXP is shown at 104. A control unit LACU is shown at 106.
In this example, each substrate visits the measurement station and
the exposure station to have a pattern applied. In an optical
lithographic apparatus, for example, a projection system is used to
transfer a product pattern from a patterning device MA onto the
substrate using conditioned radiation and a projection system. This
is done by forming an image of the pattern in a layer of
radiation-sensitive resist material on a substrate.
[0029] The term "projection system" used herein should be broadly
interpreted as encompassing any type of projection system,
including refractive, reflective, catadioptric, magnetic,
electromagnetic and electrostatic optical systems, or any
combination thereof, as appropriate for the exposure radiation
being used, and/or for other factors such as the use of an
immersion liquid or the use of a vacuum. In general the projection
system is referred to as the "lens" throughout this document, and
these terms are interchangeable. The patterning device MA may be a
mask or reticle, which imparts a pattern to a radiation beam
transmitted or reflected by the patterning device MA. Well-known
modes of operation include a stepping mode and a scanning mode. As
is well known, the projection system may cooperate with support and
positioning systems for the substrate and the patterning device in
a variety of ways to apply a desired pattern to many target
portions across a substrate. Programmable patterning devices may be
used instead of reticles having a fixed pattern. The radiation for
example may include electromagnetic radiation in the deep
ultraviolet (DUV) or extreme ultraviolet (EUV) wavebands. The
present disclosure is also applicable to other types of
lithographic process, for example imprint lithography and direct
writing lithography, for example by electron beam.
[0030] The lithographic apparatus control unit LACU controls all
the movements and measurements of various actuators and sensors,
causing the apparatus to receive substrates W and reticles MA and
to implement the patterning operations. Control unit LACU also
includes signal processing and data processing capacity to
implement desired calculations relevant to the operation of the
apparatus. In practice, control unit LACU will be realized as a
system of many sub-units, each handling the real-time data
acquisition, processing and control of a subsystem or component
within the lithographic apparatus LA.
[0031] Before the pattern is applied to a substrate at the exposure
station EXP, the substrate is processed at the measurement station
MEA so that various preparatory steps may be carried out. The
preparatory steps may include mapping the surface height of the
substrate using a level sensor and measuring the position of
alignment marks on the substrate using an alignment sensor. The
alignment marks are arranged nominally in a regular grid pattern.
However, due to inaccuracies in creating the marks and also due to
deformations of the substrate that occur throughout its processing,
the alignment marks may deviate from the ideal grid. Consequently,
in addition to measuring position and orientation of the substrate,
the alignment sensor in practice must measure in detail the
positions of many marks across the substrate area, if the apparatus
is to print product features at the correct locations with very
high accuracy.
[0032] The lithographic apparatus LA may be of a so-called dual
stage type which has two substrate tables, each with a positioning
system controlled by the control unit LACU. While one substrate on
one substrate table is being exposed at the exposure station EXP,
another substrate can be loaded onto the other substrate table at
the measurement station MEA so that various preparatory steps may
be carried out. The measurement of alignment marks is therefore
very time-consuming and the provision of two substrate tables
enables a substantial increase in the throughput of the apparatus.
If the position sensor is not capable of measuring the position of
the substrate table while it is at the measurement station as well
as at the exposure station, a second position sensor may be
provided to enable the positions of the substrate table to be
tracked at both stations. Alternatively, the measurement station
and exposure station can be combined. For example, it is known to
have a single substrate table, to which a measurement stage is
temporarily coupled during the pre-exposure measuring phase. The
present disclosure is not limited to either type of system.
[0033] Within the production facility, apparatus 100 forms part of
a "litho cell" or "litho cluster" that contains also a coating
apparatus 108 for applying photosensitive resist and other coatings
to substrates W for patterning by the apparatus 100. At an output
side of apparatus 100, a baking apparatus 110 and developing
apparatus 112 are provided for developing the exposed pattern into
a physical resist pattern. Between all of these apparatuses,
substrate handling systems take care of supporting the substrates
and transferring them from one piece of apparatus to the next.
These apparatuses, which are often collectively referred to as the
"track", are under the control of a track control unit which is
itself controlled by a supervisory control system SCS, which also
controls the lithographic apparatus via lithographic apparatus
control unit LACU. Thus, the different apparatuses can be operated
to maximize throughput and processing efficiency. Supervisory
control system SCS receives recipe information R which provides in
great detail a definition of the steps to be performed to create
each patterned substrate.
[0034] Once the pattern has been applied and developed in the litho
cell, patterned substrates 120 are transferred to other processing
apparatuses such as are illustrated at 122, 124, 126. A wide range
of processing steps are implemented by various apparatuses in a
typical manufacturing facility. For the sake of example, apparatus
122 in this embodiment is an etching station, and apparatus 124
performs a post-etch annealing step. Further physical and/or
chemical processing steps are applied in further apparatuses, 126,
etc. Numerous types of operation can be required to make a real
device, such as deposition of material, modification of surface
material characteristics (oxidation, doping, ion implantation
etc.), chemical-mechanical polishing (CMP), and so forth. The
apparatus 126 may, in practice, represent a series of different
processing steps performed in one or more apparatuses.
[0035] As is well known, the manufacture of semiconductor devices
involves many repetitions of such processing, to build up device
structures with appropriate materials and patterns, layer-by-layer
on the substrate. Accordingly, substrates 130 arriving at the litho
cluster may be newly prepared substrates, or they may be substrates
that have been processed previously in this cluster or in another
apparatus entirely. Similarly, depending on the required
processing, substrates 132 on leaving apparatus 126 may be returned
for a subsequent patterning operation in the same litho cluster,
they may be destined for patterning operations in a different
cluster, or the substrate 134 may be finished products to be sent
for dicing and packaging.
[0036] Each layer of the product structure requires a different set
of process steps, and the apparatuses 126 used at each layer may be
completely different in type. Further, even where the processing
steps to be applied by the apparatus 126 are nominally the same, in
a large facility, there may be several supposedly identical
machines working in parallel to perform the step 126 on different
substrates. Small differences in set-up or faults between these
machines can mean that they influence different substrates in
different ways. Even steps that are relatively common to each
layer, such as etching (apparatus 122) may be implemented by
several etching apparatuses that are nominally identical but
working in parallel to maximize throughput. In practice, moreover,
different layers require different etch processes, for example
chemical etches, plasma etches, according to the details of the
material to be etched, and special requirements such as, for
example, anisotropic etching.
[0037] The previous and/or subsequent processes may be performed in
other lithography apparatuses, as just mentioned, and may even be
performed in different types of lithography apparatus. For example,
some layers in the device manufacturing process which are very
demanding in parameters such as resolution and overlay may be
performed in a more advanced lithography tool than other layers
that are less demanding. Therefore some layers may be exposed in an
immersion type lithography tool, while others are exposed in a
`dry` tool. Some layers may be exposed in a tool working at DUV
wavelengths, while others are exposed using EUV wavelength
radiation.
[0038] In order that the substrates that are exposed by the
lithographic apparatus are exposed correctly and consistently, it
is desirable to inspect exposed substrates to measure properties
such as overlay errors between subsequent layers, line thicknesses,
critical dimensions (CD), etc. Accordingly a manufacturing facility
in which litho cell is located also includes metrology system MET
which receives some or all of the substrates W that have been
processed in the litho cell. Metrology results are provided
directly or indirectly to the supervisory control system (SCS) 138.
If errors are detected, adjustments may be made to exposures of
subsequent substrates, especially if the metrology can be done soon
and fast enough that other substrates of the same lot are still to
be exposed. Also, already exposed substrates may be stripped and
reworked to improve yield, or discarded, thereby avoiding
performing further processing on substrates that are known to be
faulty. In a case where only some target portions of a substrate
are faulty, further exposures can be performed only on those target
portions which are good.
[0039] Also shown in FIG. 1 is a metrology apparatus 140 which is
provided for making measurements of parameters of the products at
desired stages in the manufacturing process. A common example of a
metrology apparatus in a modern lithographic production facility is
a scatterometer, for example an angle-resolved scatterometer or a
spectroscopic scatterometer, and it may be applied to measure
properties of the developed substrates at 120 prior to etching in
the apparatus 122. Using metrology apparatus 140, it may be
determined, for example, that important performance parameters such
as overlay or critical dimension (CD) do not meet specified
accuracy requirements in the developed resist. Prior to the etching
step, the opportunity exists to strip the developed resist and
reprocess the substrates 120 through the litho cluster. As is also
well known, the metrology results 142 from the metrology apparatus
140 can be used to maintain accurate performance of the patterning
operations in the litho cluster, by supervisory control system SCS
and/or control unit LACU 106 making small adjustments over time,
thereby minimizing the risk of products being made
out-of-specification, and requiring re-work. Of course, metrology
apparatus 140 and/or other metrology apparatuses (not shown) can be
applied to measure properties of the processed substrates 132, 134,
and incoming substrates 130.
[0040] In the example of a lithographic manufacturing process, the
substrates are semiconductor wafers or other substrates to which
patterns are to be applied in a patterning step, and structures
formed by physical and chemical process steps.
[0041] In a first embodiment, at least one feature 160 may be
provided on a surface of a substrate 120, 132, 132, 134 to enable
positioning of the substrate. The feature 160 may be a specific
feature intended for alignment, or any other feature which may be
measured to allow the substrate to be aligned, e.g. before
exposure. The positioning of the substrate may be carried out using
the feature 160. The positioning includes moving the substrate in a
variety of ways, including moving the substrate large distances,
and/or making very small adjustments to the position of the
substrate. A feature 160 is shown on substrate 130 of FIG. 1 but
may equally be found on the other substrates depicted in FIG. 1.
The feature 160 may be used to align a layer of a substrate to a
previous layer (or layers) of the substrate which have already been
exposed. The feature 160 is shown as a single feature on the
surface of the substrate, but it will be understood that the
feature 160 may be part of a grid pattern and/or there may be
multiple features 160 on any single substrate layer. The location
of the feature 160 is measured to ensure that the substrate is
positioned in the correct location when exposure of the substrate
130 is carried out. As already described, any errors in the
positioning of the substrate 130 may lead to overlay errors
potentially causing yield loss of the lithographic process. As
described above, known methods for reducing overlay errors are
known and systems such as metrology system 140 and supervisory
control system SCS may already be in place to minimize overlay
error.
[0042] Although the feature 160 is placed on the substrate as
accurately as possible, during exposure of the feature 160 there
will normally be an error in the placement of the feature 160. This
can be referred to as the placement error. The placement error is
the difference between an intended placement of the feature 160 and
an actual placement of the feature 160. This means that the feature
160 is not printed exactly at the desired location. Thus, when
using the feature 160 to position a substrate 130 and aligning a
subsequent layer of the substrate (or a layer of a further
substrate), the layer will not be at the exact position where it is
expected. Thus, any resulting position corrections based on the
alignment measurements will contain the placement error.
[0043] The placement error may be determined in different ways. For
example, lens (i.e. projection system) and/or patterning device MA
distortions can cause an overlay error having a certain fingerprint
across a field (intrafield fingerprint). An overlay fingerprint is
the overlay error across the fields of the substrate. The overlay
fingerprint may vary across the fields and/or substrates because it
depends on the state of the substrate 130, projection system and/or
patterning device MA which will typically change during exposure of
substrates 130. The overlay fingerprint may change during exposure
due to the (non-uniform) temperature increases of the substrate
130, patterning device MA and/or the projection system. These
distortions within the field are typically high-order, meaning that
the centre of the field is not necessarily displaced, but the shape
of the field may be distorted. Depending on where the intended
placement of the feature 160 is on the substrate 130, this will
mean there is a placement error which varies per lot of substrates,
per substrate, per layer and even per field of the substrate.
[0044] An error in the placement of a feature used to align layers
of a substrate can lead to overlay error. An error in the placement
means that there is a difference between the intended location of
the features used to position the layers, and the actual location
of the features used to position the layers. The error in the
placement of these features can lead to each of the layers being
positioned in slightly incorrect location for exposure, thus
leading to overlay error. The automated process control (APC)
system will try to account for this error as it will control part
of the static and drifting part of the overlay error. However, the
APC system may not be able to control overlay error variations
between substrates. When overlay is critical between two layers of
a substrate, and those layers align to alignment markers in
different layers, or use different alignment models, this can
result in increased overlay variation, i.e. overlay errors. This
will reduce the yield of substrates produced by the lithographic
apparatus 100. The effect of the placement error could possibly
cancel out without affecting overlay if the layers are aligned to
alignment markers in the same layers, using the same alignment
model and settings of the system measuring the position of the
alignment markers (e.g. wavelength of radiation used to measure and
the order wherein the markers are measured). However, this is not
always possible or desirable and imposes unrealistic physical
constraints. The method described in the embodiments has fewer
constraints and thus increase design freedom.
[0045] A variation in intrafield distortions and/or translation
and/or rotations of the field during placement of the feature 160
results in variation during exposure of layers of the substrate
which are aligned to that feature 160. When the position of the
feature 160 is measured, the displacement of the feature may be
interpreted as an overlay error and thus, the field centres will be
erroneously "corrected" based on a translation error. Thus the
placement error may cause an incorrect "correction" which affects
alignment of the substrate which contributes to overlay error.
Presently known systems do not adequately account for the placement
error.
[0046] In an embodiment, a method is provided for determining a
position of a feature reference to a substrate. The method
comprises measuring a position of the feature, wherein the feature
is configured to enable positioning of the substrate. The method
further comprises receiving an intended placement of the feature
and determining an estimate of a placement error. The placement
error is the difference between the intended placement of the
feature and an actual placement of the feature. The placement error
can be determined based on knowledge of a relative position of the
first reference feature reference to a first layer with respect to
a second reference feature reference to a second layer, wherein the
first layer and the second layer are on a substrate. The method
further comprises determining an updated position for the feature
using the estimate of the placement error and the measured position
of the feature. The feature 160 being referenced to a substrate 130
may mean that the feature is on a substrate 130, e.g. located on a
layer of a substrate 130. The first reference feature and the
second reference feature being referenced to a first layer and
second layer respectively may mean that the first reference feature
is on the first layer and the second reference feature is on the
second layer.
[0047] By using both the measured position of the feature and
determining an estimate of the placement error, a more accurate
position of the feature (i.e. the updated position) can be
determined. As described, despite the above described known systems
for correcting and reducing positioning errors, there is a further
problem that errors can be introduced when the feature is formed on
the substrate. Using the method described above allows the system
to account for the error in forming the feature on the substrate
(placement error) which is later used to position the substrate.
This is particularly beneficial as it can be used as part of a
feedforward and/or feedback system to more accurately position
further layers of the substrate and/or further substrates
respectively. The updated position may be used for controlling a
position of a substrate. This may be particularly useful for
example for a step of patterning the substrate. For example, this
could be used in a manufacturing process, such as a lithographic
manufacturing process, of the type described in relation to FIG.
1.
[0048] The method allows for the error in placing the feature 160
on the substrate 130 to be accounted for. The feature may be
provided on a layer of any of the substrate 120, 130, 132, 134
shown in FIG. 1. The method allows the error to be determined as
part of a feedback loop or feedforward loop for positioning the
layer of the substrate 130 comprising the feature 160, and/or
further layers of the same substrate 130 and/or a layer of a
further substrate 130. The feedback loop may use the updated
position for determining an updated position for further
substrates. The feedforward loop may use the updated position for
exposing further layers on the same substrate, i.e. the substrate
comprising the first reference feature and second reference
feature. Thus, the updated position may be used as part of a
feedback and/or feedforward loop. The method is beneficial even for
a single layer of the substrate 130 comprising the feature 160
because the substrate 130 is more accurately positioned for
exposing the layer comprising the feature 160. For each feature
160, there might be a corresponding correction for the placement
error of the feature 160.
[0049] The updated position can be used as an input for the
alignment model described above. In other words, when the position
of a feature 160 is measured, the updated position can be used as
the input for the alignment model rather than the measured position
of the feature 160. In this way, the placement error is accounted
for. Using the updated position means that the placement error does
not impact the alignment modelling and alignment corrections during
exposure of the layer of the substrate 130 and also during exposure
of further layers of the substrate 130 and/or further substrate(s).
Thus, the method may be a feedforward method which uses the updated
position for determining placement of further layers and/or
substrates.
[0050] The method is useful for determining the updated position of
the feature which can be used in various ways is herein described.
Most simply, the updated position of the feature 160 may be used to
position a substrate 130 on the basis of the updated position of
the feature 160. The substrate 130 may be a substrate 130
comprising the first layer and the second layer. The feature 160
may be positioned on the first layer or the second layer. Thus, the
substrate 130 comprising the feature 160 on the first layer or the
second layer, for example, may be positioned to align the first
layer or the second layer of the substrate 130 respectively as
desired. The method may further comprise exposing the first layer
of the substrate 130 to conditioned radiation. This means that the
first layer can be more accurately positioned to take into account
the placement error of the feature 160 used to align the substrate
130.
[0051] Alternatively, the feature 160 may be located on another
layer of the substrate 130 comprising the first layer and/or the
second layer, i.e. the feature 160 may be on the same substrate 130
as the first reference feature and the second reference feature but
on a different layer. Thus, the method may be used to position a
further layer on the same substrate based on the placement error
calculated for a feature 160 on a previous layer. Alternatively,
the feature 160 may be on a layer of a different substrate i.e. the
feature 160 may be on a further substrate for which no measurement
of the first and second reference feature is performed. Thus, the
method may be used to position a further substrate based on the
placement error calculated on a previous substrate. In other words,
the position of the feature may be measured on a substrate
different from the substrate associated with the determined
estimate of the placement error. Thus, the error estimated for one
substrate can be used to update a position of a feature 160 on
another substrate.
[0052] The feature 160 may be on the first or the second layer of
the further substrate. Thus, the feature 160 may be placed on an
equivalent layer to the first layer or the second layer, but on a
different substrate. For example, the first layer may in fact be a
fourth layer to be exposed on the substrate and thus, the first
reference feature may be placed on the fourth layer of a substrate
and the feature may be placed on the fourth layer of another
substrate. Alternatively, this may apply to the second layer rather
than the first layer. It will be understood that the example of the
fourth layer could be replaced with any layer, including the first,
second, third and so on.
[0053] The estimate of the placement error may be applied to
selected features on selected layers and/or substrates. Thus, it is
possible to preselect the features to which the placement error is
applied. E.g. the updated position and/or estimate of the placement
error could be applied during exposure of all layers of all
substrates in one lot, or even several lots.
[0054] As described above, the method for determining the updated
position of the feature 160 may be particularly useful because it
can be used in a feedforward or feedback system to determine
positioning of further layers and/or further substrates. This means
that the placement error for one feature 160 (or for several
features on one layer of a substrate 130) may be used to more
accurately position further layers on the substrate and/or
substrates. This is beneficial because it is not necessary to
determine the placement error for each layer or even for each
substrate. Furthermore, once the placement error has been
determined, this can be used for further alignments even after the
layer comprising the feature 160 has been exposed. Advantageously,
this means that measurements to determine the placement error may
not be required on further layers and/or substrates. Reducing the
number of measurements reduces the time taken to produce
semiconductor devices (i.e. fully processed substrates) which is
preferable. In general, the placement error might be used for
determining the placement error of further features, even if
further measurements or models are used, and can still be
beneficial in reducing the number of measurements and/or amount of
modelling required to determine further placement errors/updated
positions.
[0055] The estimate of the placement error may be determined in
various different ways. As already described, the estimate is based
on a knowledge of a relative position of a first reference feature
referenced to a first layer on a substrate with respect to a second
reference feature referenced to a second layer of the substrate. In
other words, the placement error is calculated using a feature from
two different layers of a substrate. As indicated above, the first
layer and the second layer may be different from the layer on which
the feature 160 is located. The first layer is a different layer
than the second layer such that the overlay can be determined
between the first layer and the second layer. The first layer and
the second layer may be adjacent to each other, or may have one or
more layers between them.
[0056] The first reference feature, the second reference feature
and/or the feature 160 may be a grating. The features may otherwise
be referred to as marks. The first reference feature and the second
reference feature may be the same type of feature as each other.
The first reference feature and the second reference feature may
not be of the same type as the feature 160 for which the placement
error is estimated. For example, the first reference feature and
the second reference feature may not be used, or capable of being
used, to align the substrate 130. The first reference feature
and/or the second reference feature may be a feature used to
measure overlay, e.g. the first reference feature and the second
feature may be gratings, optionally, overlay marks or optionally
product features usable to determine an overlay error. The first
reference feature and/or second reference feature may be overlay
marks configured to provide overlay feedback to the APC system.
Additionally or alternatively, the feature 160 may be a grating,
e.g. an alignment mark.
[0057] The method may comprise measuring the first reference
feature and the second reference feature to determine an overlay
error between the first layer and the second layer. Thus, the
method may comprise directly measuring the first reference feature
and the second reference feature to determine the placement error.
The first reference feature and the second reference feature may be
used to determine the overlay error between the first layer and the
second layer. Thus, the overlay error may effectively be measured
at the location of the first reference feature and the second
reference feature. This could be done for example by the APC system
described above. For example, results 146 relating to the
measurements of the first reference feature and the second
reference feature may be sent from the metrology apparatus 140 to
the APC system. The method may use the measured overlay error to
determine the estimate of the placement error. For example, the
estimate of the placement error may be the same as the measured
overlay error i.e. the estimate of the position error and the
overlay error may be one-to-one. Alternatively, the estimate of the
placement error may be a function of the measured overlay error, or
may comprise the measured overlay error. Processing steps may be
required to determine the placement error based on the overlay
error. The overlay error may not be equal to the placement error,
for example, due to different sensitivities of the feature 160 and
the reference feature regarding variations in process conditions
and projection system aberrations.
[0058] An exemplary implementation of a method in accordance with
an embodiment is depicted in FIG. 2. In S10 the position of the
feature 160 is measured. This step could be carried out before,
after or at the same time as step S11. In S11, the first reference
feature and the second reference feature are measured as described
above. The measured first reference feature and second reference
feature may be used to determine the estimate of the placement
error in S12. In S13, the measured position of the feature from S10
and the estimate of the placement error from S12 may be used to
calculate an updated position of the feature. As previously
described, the feature may be on one of the first layer or the
second layer, the feature may be on another layer of the substrate
comprising the first layer and the second layer (i.e. a further
layer of the same substrate), or the feature may be on a layer of a
substrate not comprising the first layer and the second layer (i.e.
a layer of a further substrate). Thus, the updated position of the
feature 160 can be used to position any of the layers comprising
the feature 160 in S14.
[0059] Alternatively, the method may further comprise modelling an
overlay error between the first layer and the second layer and
determining the first and second feature using the modelled overlay
error. The method may comprise using an overlay model to determine
the overlay error across at least a part of the substrate 130. The
modelled overlay error across the substrate 130 may be used to
extract the modelled position of the first feature and the second
feature. The overlay error may be modelled in various different
ways. For example, the method may comprise receiving context
information and/or lithographic apparatus information, and using
the context information and/or lithographic apparatus information
to model the overlay error. The context information and/or
lithographic apparatus information relates to measured and/or
modelled deformation of at least one of the substrate, a mask
and/or the projection system. The context information and/or
lithographic apparatus information may include results 146 of
measurements from the metrology system 140, and/or from the
lithographic apparatus LA 100. Modelling the overlay error may
comprise using a predetermined value. This could be based, for
example, on previous overlay data, on average overlay errors for
multiple substrates or lots of substrates or average overlay errors
between particular layers of substrate.
[0060] The method may use the modelled overlay error to determine
the estimate of the placement error. Measurements may be taken from
convenient measurement location(s) on the substrate 120. Modelling
the overlay to determine the position of the first reference
feature and the second feature has the further advantage that the
location of the first reference feature and the second reference
feature are not limited to being near the feature 160 and the first
reference feature and second reference feature may be located
elsewhere away from the feature 160. The method may use the
modelled overlay error to determine the estimate of the placement
error. For example, the estimate of the placement error may be the
same as the modelled overlay error, i.e. the estimate of the
position error and the overlay error may be one-to-one.
Alternatively, the estimate of placement error may be a function of
the modelled overlay error, or may comprise the modelled overlay
error. Processing steps may be required to determine the placement
error based on the overlay error.
[0061] An exemplary implementation of a method in accordance with
an embodiment is depicted in FIG. 3. In S20 the position of the
feature 160 is measured. This step could be carried out before,
after or at the same time as either of the steps in S21 or S22. In
S21, context information and/or lithographic apparatus information
may be received as described above and this may be used to
determine an overlay error in S22. Determining the overlay error
may comprise calculating a model of the overlay error between a
first layer and a second layer to calculate a modelled position of
a first reference feature and a position of a second reference
feature. The estimate of the placement error can then be determined
based on the modelled positions of the first reference feature and
the second reference feature in S23. In S24, the measured position
of the feature from S20 and the estimate of the placement error
from S23 can be used to calculate an updated position of the
feature. As previously described, the feature 160 may be on one of
the first layer or the second layer, the feature 160 may be on
another layer of the substrate comprising the first layer and the
second layer (i.e. a further layer of the same substrate), or the
feature 160 may be on a layer of a substrate not comprising the
first layer and the second layer (i.e. a layer of a further
substrate). Thus, the updated position of the feature 160 can be
used to position any of the layers comprising the feature in S25.
It is noted that certain steps of FIG. 3, e.g. S20, S24, S25 may be
carried out in the same way as the corresponding steps of FIG. 2,
e.g. S10, S13 and S14 respectively.
[0062] In further detail, for each exposed lot, only a few
substrates may be selected and measured on the metrology apparatus
140 to determine the error of overlay-targets on the substrate. The
overlay-targets may be marks or features which are similar to the
first reference feature and the second reference feature. These
measurements can be input to the APC system to determine feedback
overlay corrections for future exposures. Since only a few
overlay-targets may be measured per lot, e.g. a few hundred, an
extrapolation and/or interpolation can be used to estimate the
overlay fingerprint for each field for each substrate as an input
for the APC system. The extrapolation and/or interpolation from a
few hundred points per substrate can be done by fitting a
mathematical model over measured points. The resulting overlay
fingerprint can be used to determine a modelled first reference
feature position and a modelled second reference feature position
for determining the feature 160.
[0063] The overlay fingerprint may be a product of the existing APC
systems. The estimate of the placement error for each feature 160
can be estimated as a function of the local overlay error:
f.sub.1(OverlayFingerprint(x,y)). This may provide a unique
estimate of the placement error for each unique overlay
fingerprint. There may be a unique overlay fingerprint per
substrate table (for example, because the APC system has a
particular correction loop for a particular substrate table), per
lot, or per substrate depending on the overlay control method which
is used to determine the overlay fingerprint. As described, the
simplest function would be a multiplication by 1, where the
estimate of the placement error is estimated to be the same as the
overlay error. More accurate estimations of f.sub.1 can be
determined by correlating overlay errors with placement errors in
either experiments or simulations. The overlay fingerprint can
optionally be refined by using context information and/or
lithographic apparatus information, e.g. the results from
f.sub.1(OverlayFingerprint(x,y)) can be refined using context
information and/or information from the lithographic apparatus LA
of 100 f.sub.2(Context information and/or lithographic apparatus
information) The refinement can, for example, result in placement
error corrections per substrate where overlay fingerprint
information is only available per substrate table and/or lot.
Refinement can also result in a more accurate estimate of the
placement error per feature 160.
[0064] To reduce the amount of measurements needed, typically the
overlay corrections can be averaged per lot or substrate table
instead of per substrate. Heating of the patterning device MA
and/or a projection system are known to increase errors. As
described, these errors can result in a placement error when
forming a feature 160. Overlay measurements can be carried out on
one or more substrates per lot, e.g. 4 substrates per lot. To
refine the results, a function f.sub.2(Context information and/or
lithographic apparatus information) can be used to extrapolate the
overlay fingerprint to determine what the fingerprint is expected
to be for other layers or substrates not measured. A part of this
calculation can use context information and/or lithographic
apparatus information referred to above, including parameters
related to patterning device MA and/or projection system heating.
This enables determination of a unique estimate of the placement
error for each feature per substrate while only 4 substrates were
measured.
[0065] Alternatively, corrections can be determined per substrate,
as herein described. The correlation between the placement error
and the overlay fingerprint may depend on the parameters included
in the context information and/or lithographic apparatus
information. The context information and/or lithographic apparatus
information may include, but is not limited to, substrate table
and/or projection system dynamics, and heating effects of the
patterning device MA and/or the projection system and/or a
substrate. The context information and/or lithographic apparatus
information can be measured (i.e. logged) or can be modelled. For
example only, the feature 160 is likely to have a different design
to the first reference feature and to the second reference feature.
This means that the light used to image the feature may take a
different path through the projection system than the light used to
image the first reference feature and the second reference feature.
Therefore, a projection system aberration may have a different
effect on the feature 160 and the first and second reference
features. The different effects can both be measured or simulated
(i.e. modelled) for several aberrations and designs. During
exposure the projection system aberrations may be measured and this
information can be combined with the measured/modelled context
information and/or lithographic apparatus information to refine the
estimate of the placement error per feature 160.
[0066] The temperature of the projection system may change whilst
multiple substrates are exposed within a lot, i.e. in a batch. More
specifically, the projection system temperature generally increases
within a lot from the first substrate to the last substrate. In
spite of arrangements to maintain a constant projection system
temperature, a small temperature change may occur (e.g. depending
on the illumination conditions) which is nevertheless significant
for forming patterns with very small features. For example, it is
know that relatively intense illumination can have significant
heating effects especially when there are extreme dipole
illumination settings which may induce projection system heating.
The heating of the projection lens may lead to introduction of lens
aberrations, typically referred to as Zernike aberrations which are
associated with characteristic imaging effects. For example a
Zernike Z7 aberration is referred to as coma and typically
associated with imaging shift effects; e.g. features are printed at
a location which is shifted with respect to a desired (nominal)
location.
[0067] When structures, such as overlay marks, alignment marks,
and/or product features have high sensitivities to Zernike
aberrations, the structures will be printed on the substrate with
an unintended shift. As the temperature of the projection system
changes, the unintended shift will change, e.g. drift, throughout
the lot. The shift can be very dynamic and may depend on many
parameters, which means that it is not possible to apply process
corrections (for example, using APC) to the entire lot to
sufficiently account for the effects of the shift.
[0068] Various correction methods based on prediction of the lens
heating evolution may be used to reduce or minimize the effects of
temperature changes in the projection system. However, even if
these methods are used, errors relating to the temperature change
across the projection system (which may be referred to as
projection system induced errors) may still remain (for example due
to the limited accuracy of such a lens heating prediction method).
When the exposed, i.e. printed, structures are sensitive to (at
least one) Zernike aberration(s), the projection system induced
errors may cause an image shift. Furthermore, different structures
at different sizes have different sensitivities. In other words,
different structures may respond to the temperature changes in the
projection system in different ways, which makes it even harder to
compensate for temperature changes. For example, different types of
structure, e.g. product features, alignment marks and/or overlay
marks, may have different sensitivities. Even different marks of
the same type (i.e. which may be used for a similar purpose) for
example, two alignment marks, may have different Zernike
sensitivity values. In this context, the Zernike sensitivity value
is an indication of the sensitivity of the mark to
aberration/temperature changes in the projection system.
[0069] The projection system induced error, e.g. translation drift,
could occur when variation of temperature in the projection system
occurs and alignment marks with a high sensitivity to aberrations
are used. This issue may be a particular problem when certain types
of feature are being exposed, for example, when creating memory
(DRAM) because the layers may be exposed using extreme dipole
illumination conditions. It is generally desirable to reduce the
overall imaging shift error between layers, e.g. the overlay error.
Even relatively small potential overlay drift of 1.5 nm for
example, due to projection system induced errors are undesirable
and in some cases, unacceptable.
[0070] In an embodiment, a first mark and a second mark for a
single layer mark are designed such that the shifts in the first
mark and/or the second mark which occur during the exposure of this
single layer mark with the first mark and the second mark due to
projection system heating are indicative of the imaging shift
associated with the projection system heating. As described below,
relative shifts between the first mark and the second mark and/or a
portions of either mark may be determined for a layer of a
substrate and may be used for controlling positioning of a further
layer of the substrate, e.g. the second layer. Thus, the projection
system induced errors may be corrected for in further
layers/substrates. This will have the benefit of reducing errors in
the marks printed on the substrate. For example, this may reduce
the error in placement of the alignment mark such that the
alignment mark is more accurately placed to the reference
structure, like device pattern, which can reduce overlay and
improve throughput. The relative shift is the difference between
the absolute distance between a first mark and a second mark in one
single layer mark and is mostly contributed by the aberration
sensitivity difference between the first and second mark.
[0071] As already described, it can be beneficial to more
accurately position an alignment mark on a layer of a substrate for
positioning the substrate. It is known that different structures,
for example, an alignment mark and a product feature, may be
affected by variations in the projection system in different ways.
The present method takes advantage of the difference in the effect
on different types of structure. Thus, in a second embodiment a
method for controlling positioning of a substrate is provided. The
method comprises providing a substrate with a first mark and a
second mark on one layer of the substrate. The first mark is
different from the second mark. The method further comprises
determining a relative shift of the first mark with respect to the
second mark. The first mark and the second mark may be on the same
layer, and may thus, be collectively referred to as a single layer
exposure mark. The method comprises controlling positioning of the
one layer of the substrate, a further layer of the substrate or a
layer of a further substrate based on the determined relative
shift. Optionally, the method further comprises determining a
projection system induced error using the determined relative shift
[for example often a linear relationship exists between a Zernike
aberration and the determined relative shift. Thus, the step of
controlling position of a substrate may be carried out using the
relative shift and/or the projection system induced error.
Knowledge of the relationship allows determination of the
projection system induced error (aberration) based on the
determined relative shift. For example, in more detail, the
relative shift can be determined by lens aberration (Zernikes) and
aberration sensitivity. For example, for lithographic effects which
are linear with aberration, the sensitivity of nth order Zernike
may be:
displacement of nth order - the displacement of an ideal lens nth
order Zernike ##EQU00001##
[0072] The first mark may otherwise be referred to as a first
pattern or a first mark pattern. The second mark may otherwise be
referred to as a second pattern or a second mark pattern.
[0073] FIGS. 4A and 4B depict an example cross section of the first
mark and the second mark on the one layer of the substrate. The
depiction in FIGS. 4A and 4B will be described in further detail
below, but it is noted that the specific details and relative sizes
shown are only exemplary.
[0074] The first mark is different from the second mark. This may
mean that the first mark and the second mark have different
sensitivities to an aberration in the projection system, wherein
the projection system is used to expose the first mark and the
second mark simultaneously. The first mark and the second mark may
differ in various ways to provide the different sensitivities.
[0075] In the example shown in FIGS. 4A and 4B, the first mark may
have multiple first portions and the second mark may have multiple
second portions. In other words, each mark may comprise several
portions, i.e. several features. It is not necessary for the first
mark and the second mark to each comprise several portions.
However, this can be beneficial because it can be easier to detect
the shift of the second mark pattern with respect to the first
mark. In other words, an average relative shift, which may be based
on the relative shift of multiple corresponding portions, may be
used to more accurately determine the shift. This is particularly
useful for diffraction based measurements described below. The
portions which make up each mark may be substantially uniform.
Thus, the portions used for the first mark may all be affected by a
projection system aberration in the same way, and/or the portions
used for the second mark may all be affected by a projection system
aberration in the same way. This means that it is simpler to
predict how the projection system aberration will affect the first
mark and/or the second mark.
[0076] In the example shown in FIGS. 4A and 4B, the wider portions
are part of the first mark and the narrower portions are part of
the second mark. The width of the portions can affect the
sensitivity to aberrations in the projection system such that the
portions of the first mark have different sensitivity to the
portions of the second mark. Additionally or alternatively the
sensitivity of the portions may be affected by diffracted pattern
difference of exposure (DUV exposure light) and measurement (SMASH
WA sensor), due to different patterns (segmentation).
[0077] The portions may form a grating. The first mark and the
second mark are to be exposed together in the one layer of the
substrate. The effect of projection system heating may be present
on at least part of the one layer.
[0078] Different patterns are indicated in FIGS. 4A and 4B to
distinguish between the first mark and the second mark. The
patterns shown in these Figures are for distinguishing between the
two types of mark only.
[0079] However, as indicated above, the first mark and the second
mark may have different sensitivities and this may be due to a
variety of reasons. An example of the different types of portion
used for the first mark and the second mark is shown in FIG. 5. As
shown, the first mark may comprise multiple first portions and the
second mark may have multiple second portions. As shown, at least
one of the second portions may comprise a plurality of elements. In
other words, the second portion may be segmented into elements. The
pitch between the second portions may be larger than the pitch
between the plurality of elements. In other words, the distance
between each of the second portions may be larger than the distance
between elements of the second portions. The pitch between the
plurality of elements of the second portion may be approximately
the same as the pitch of product features. Thus, the second mark
may be a product feature or a feature having a similar response to
the projection system induced error as a product feature.
[0080] A first portion may comprises fewer elements than a second
portion.
[0081] Furthermore, the first portion may not be segmented at all.
Thus, at least one of the first portions may comprise only a single
element. This is indicated by the shape of the first portions shown
in FIG. 5. Thus the first mark may be an alignment mark or an
overlay mark. The pitch between the first portions is much greater
than the pitch between individual elements of the second
portion.
[0082] A single element of a first portion may be larger than a
single element of a second portion. This means that for example,
when viewed in an X-Y plane, as is shown in FIG. 5, an element of
the first portion may have a greater cross sectional area than an
element of a second portion. Thus, the different sizes of the
elements of the first portion and the second portion may have
different sensitivities. A single element of a first portion may
correspond in size to the plurality of elements making up a second
portion. This means that when viewed in an X-Y plane, a parameter
around the element(s) of a first portion may be of substantially
similar size to a parameter around the element(s) of a second
portion. This is depicted in FIG. 5, because although a plurality
of elements may be used to make up portions of the first and/or
second mark, each of the portions of the first mark and the second
mark have similar lengths and widths overall.
[0083] Additionally, the first portions may be substantially
consistent in shape and pitch, and the second portions may be
substantially consistent in shape and pitch. This means that the
first portions are generally the same as each other and have a
consistent distance between portions, and the second portions are
generally the same as each other and have a consistent distance
between portions. The markers may be considered to have a grating
like configuration, in other words, the markers may typically have
periodic repetition of a portion as depicted in FIGS. 4A, 4B and 5.
A periodic aspect of the portions may be useful in particular when
using diffractive based measurements on the markers to determine
the relative shift between the first marker and the second
marker.
[0084] Although FIG. 5 depicts that the first mark has multiple
first portions and the second mark has multiple second portions,
this is for example only. The first mark may have more portions
than are shown in FIG. 5, or may have fewer, or even one. The
second mark may have more portions than are shown in FIG. 5, or may
have fewer, i.e. one.
[0085] The first mark and the second mark depicted in FIGS. 4A and
4B are for example only but can be used to illustrate various
features relating to the first mark and the second mark. For
example, the first mark and the second mark may overlap. This means
that when the substrate is viewed perpendicular to the surface of
the substrate, the first mark and the second mark appear to be
overlapping at least in part. As will be described, this may mean
that the first portions and the second portions are interlaced, at
least for the overlapping parts of the mark. However, even when
overlapping/being interlaced the individual portions of each mark
do not overlap. Thus, none of the first portions are in contact
with any of the second portions.
[0086] It is not necessary that the first mark and the second mark
overlap, for example, the first mark and the second mark may be
near each other or adjacent to one another, or aligned along one
edge. The relative shift between the first mark and the second mark
may still be determined without an overlap, but having the marks
overlap, i.e. by having the first mark extend across at least part
of the second mark, may mean that the shift can be more accurately
determined. In general, extension of marker, for example, a grating
like marker, enables use of diffraction based metrology, which by
definition averages across the whole (at least illuminated) part of
the marker. Thus, the overlap may improve accuracy as measurement
error may then also be scaled down.
[0087] The first mark and the second mark may optimally be at the
same level, i.e. exposed at the same time. Ideally, the first mark
and the second mark are in the resist (right after exposure) and
may be measured in the resist).
[0088] As shown in the FIGS. 4A and 4B, the first mark and the
second mark may be interlaced, or more specifically, the first
portions and the second portions may be interlaced. In other words,
the first portions and the second portions may be alternating, as
shown in FIGS. 4A and 4B. This may occur due to the overlapping
nature of the first mark and the second mark. The first portions
and the second portions may be interlaced without having the first
portions and the second portions overlap i.e. the first portions do
not touch the second portions. In other words, the first mark and
the second mark may overlap, but the first portions may not contact
or overlap with the second portions. This is preferable because it
may not be possible to detect the relative shift of any of the
second portions relative to a corresponding first portion if part
of the first portion and the second portion are effectively in
contact with each other.
[0089] The relative shift between the first mark and the second
mark is depicted in FIGS. 4A and 4B. FIG. 4A depicts an example of
how the first mark and the second mark would be provided if the
first mark and the second mark were exposed on the one layer of the
substrate when no projection system aberration was present. As
shown in FIG. 4A, there is a distance, d, between the centre point
of a portion of a first mark and a centre point of a corresponding
portion of a second mark. In this example, the corresponding first
portion and second portion are adjacent to one another. The
distance, d, is the distance between the corresponding portions of
the first mark and the second mark when there is no projection
system aberration.
[0090] When there is a projection system aberration, the first mark
and the second mark are affected (i.e. shifted). Because the first
mark is different from the second mark, the first mark and the
second mark are affected in different ways by the projection system
aberration. Thus, the distance between the corresponding portions
of the first mark and the second mark is not the same as in FIG.
4A. As shown in FIG. 4B, the distance between the corresponding
portions of the first mark and the second mark when there was a
projection system aberration during exposure is s. As is clear from
FIGS. 4A and 4B, distance s is not the same as distance d. In this
example, the distance between the first portion and the
corresponding second portion, s, is greater due to the projection
system aberration than the distance between the first portion and
the second portion, d, when there is no projection system
aberration. It is noted that for other combinations of different
marks, the distance s may be smaller than the distanced. Thus,
there is a relative shift between the first mark and the second
mark due to a projection system aberration.
[0091] The relative shift depends on the state of the projection
system, so that in a case of projection system heating, drift will
occur throughout the lot of substrates (i.e. intralot drift). Also
the starting state of the projection system will be dependent on
the usage of the projection system prior to the lot. Therefore, the
actual shift may vary dynamically from one lot to another, or from
one substrate to another. As will be described below, using the
first mark and the second mark of an embodiment of the present
invention, the relative shift can be determined for each lot and
each substrate in the lot. The determined relative shift can be fed
forward to the next layer(s) for a substrate specific
correction.
[0092] The relative shift between the first mark and the second
mark can be determined in a variety of different ways. For example,
the method may determine the relative shift by measuring a position
of the first mark and a position of the second mark after they have
been exposed and comparing the measured positions to an expected
distance between the first mark and the second mark. Thus, the
method may comprise measuring the position of the first mark and
the second mark and calculating the distance between the first mark
and the second mark. The relative shift may then be determined
using the calculated distance between the first mark and the second
mark and an expected distance between the first mark and the second
mark. It is noted that the distance between the first mark and the
second mark may be the distance between a first portion and a
corresponding second portion, or may be the average (e.g. mean)
distance between first portions and corresponding second
portions.
[0093] The first mark and the second mark may be designed in a way
that allows the projection system heating related relative image
shift between the first mark and the second mark to be measured
using known measurement systems after the marks are exposed. For
example, the measurements may be done using Integrated Metrology
(IM) or Stand Alone Metrology (SA), typically based on diffractive
measurements. Advantageously, the measurements can be carried out
on the first mark and the second mark in resist (i.e. before the
substrate is processed further, e.g. subjected to etching and/or
deposition processes) which means that little or no significant
mark degradation is to be expected. This means that the accuracy
and precision may be much higher than when measurement of an etched
mark is used.
[0094] Other methods for determining the relative shift may be
used. In another example, the relative shift is determined using
diffraction based measurement. A marker comprising portions (which
may form a grating), which allows the use of diffraction based
measurements which are common in the lithographic industry. A
diffraction based measurement method and system is known and herein
incorporated by reference in its entirety from U.S. Pat. No.
9,134,256B2. A diffraction based measurement may integrate the
shift error across all portions (e.g. an entire grating) and hence
use determine and use of an average relative shift. Furthermore,
the idea of mark measurement is known from WO2014146906 A2 which is
herein incorporated by reference in its entirety. WO2014146906 A2
discloses measuring marks in the resist and feeding forward the
measured information to the next exposure as a substrate specific
correction.
[0095] Optionally, a third mark, which is on a different layer to
the first mark and the second mark, may be provided. The position
of the third mark can be determined and the position may be used
with the determined relative shift to control positioning of the
different layer of the substrate and/or any other layer of the
substrate. The third mark may be a known, standard mark, such as an
alignment mark.
[0096] An example implementation for the above described method is
shown in the flow chart of FIG. 6. In step S30, a substrate with a
first mark and a second mark is provided. It is noted that this may
include additional steps of exposing the first mark and/or the
second mark as will be further described. Additionally, this step
may include selecting/designing the structures used for the first
mark and/or the second mark. Thus, it is possible to select a first
mark and/or a second mark which will have a desired relative shift.
This may be beneficial, because a specific first mark and/or second
mark may be chosen to allow the relative shift to be more easily
and/or more accurately determined so that a more accurate estimate
of the relative shift and/or projection system induced error can be
determined.
[0097] In a further step S31, the relative shift is determined.
This may be done using any appropriate method. Examples include
those described above, i.e. using measurements of the position of
the first and the second mark, or using diffractive based
measurements. Optionally, the relative shift can be used to
determine a projection system induced error as shown in step S32
For example, as described above, there often exists a linear
relationship between a Zernike aberration and the determined
relative shift. Knowledge of the relationship allows determination
of the projection system induced error (aberration) based on the
determined relative shift. It is noted that more complicated
relationships may be determined and used.
[0098] The determined relative shift and/or projection system
induced error can then be used to control positioning of one layer
of the substrate, a further layer of the substrate or a layer of a
further substrate as in step S33. The determined relative shift
and/or projection system induced error can optionally be used as
part of a feedback or feedforward system. The determined relative
shift and/or the determined projection system induced error can be
used in a feedback loop to control positioning of a layer of a
further substrate and/or in a feedforward loop to control
positioning of a further layer of the same substrate. This means
that the determined relative shift and/or the determined projection
system induced error can be used to control positioning of other
layers of the substrate or layers of further substrates and the
other layers/further substrates can be exposed taking into account
the projection system induced error. Step 33 includes controlling
the positioning of a substrate using feedforward and/or feedback
methods. After the layer has been positioned in accordance with the
above, it can be exposed to radiation and the above described
method should reduce or prevent errors due to projection system
aberrations.
[0099] Advantageously, the feedback and feedforward loops means
that the determined projection system induced error and/or the
determined relative shift only needs to be determined for a single
layer and/or substrate and the determined projection system induced
error and/or relative shift can then be used to correct/improve
positioning of further layers and/or substrates.
[0100] The projection system induced error may refer to any error
due to projection system aberration. This may comprise projection
system drift and/or projection system heating. For example, the
projection system drift may include intrasubstrate drift
granularity (i.e. from a first exposed field to a last exposed
field). This may require denser measurements per substrate than
would otherwise be needed. Intrasubstrate correction of the
projection system induced error can also be improved by careful
distribution of a number of first marks and second marks provided
per substrate and the number of substrates per lot, ideally in
addition to a good estimation model. For example, considering an
example using a substrate alignment mark, aberration impact on a
substrate alignment mark may be considered as translation-X and
translation-Y. A large number of points are not needed to calculate
translation per substrate. Depending on intra lot drift,
measurement scheme may change, as indicated below. Using this
method can avoid undesirable increases in the measurement time.
[0101] The relative shift and/or the projection system induced
error can be determined for multiple layers and/or substrates. For
example, all substrates in the lot can be measured, or only a few
of the substrates, which may optionally be evenly spread throughout
the lot.
[0102] The second embodiment can be applied using the difference
between any combination of different structures, such as overlay
marks, alignment marks and product features, etc. In the example
above, the first mark may be an alignment mark. However, the first
mark may alternatively be an overlay mark. The second mark may be a
product feature or a feature having a similar response to the
projection system induced error as a product feature. In other
words, the second mark may be any structure which is affected by an
aberration in the projection system in the same or a similar way as
a product feature would be affected. The structure used for the
second mark does not have to be an actual product feature. It will
be understood that the first and second terminology used in
relation to the marks is simply used for the purposes of
distinguishing between the different marks. Thus, the first mark
could be replaced with the second mark and vice versa. The first
mark and/or the second mark and/or the first mark overlapped with
the second mark may have the same overall dimension of known
overlay marks. The first mark and/or the second mark may have the
pitch of known marks, such as known alignment marks, and may be
measurable using known measurement systems.
[0103] Using different types of mark mean that aberration related
drifts and the offsets between these marks can be corrected. If the
static projection system aberration exists, the methods of the
present embodiment can measure this static offset using an
alignment mark the first mark and another structure, such as an
overlay mark or a product mark as the second mark. The static
non-zero offsets can be minimized using the above described methods
such that non-zero offsets will not need to be calibrated.
Different types of mark, such as alignment marks, overlay marks and
product features or the like may have different pitches. Therefore,
it may be difficult of impossible to match the different types of
mark such that they overlap but do not touch. In the present
embodiment, the methods described above should allow for this using
measurements and corrections for the differences in pitch.
[0104] One of the advantages of the present embodiment is that
dense sampling is not required to obtain the necessary relative
shift described above. Therefore, the measurements can be carried
out using systems already in place as described above, i.e.
metrology systems which are already integrated in the litho tool
100. Furthermore, this means that it is not necessary to have a
large number of marks. The layer comprising the first mark may
comprise any number of suitable first marks. The layer comprising
the second mark may comprise any number of suitable second marks.
Preferably, there are the same number of first marks and second
marks. For example, the layer comprising the first mark may
comprises at least five to ten first marks and the layer comprising
the second mark may comprise a corresponding number of second
marks, i.e. the same number of second marks. In other words, there
may be the same number of first marks and second marks on the
relevant layers. The projection system induced error is generally a
translation error in case of standard inter field wafer alignment
whose layout is one mark per field with many fields, which means
that a small number of marks, e.g. five to ten, may be sufficient.
Furthermore, linear and higher order parameter errors can be taken
into account by using additional marks in a field. Thus, there can
be more than ten first marks and more than ten second marks on the
relevant layer(s).
[0105] The methods described in the second embodiment may be used
to determine the relative shift and/or the projection system
induced error as described above. As already indicated, the
projection system induced error can be an issue when any marks are
created on the layer of the substrate. Thus, when determining the
updated position for the feature using the methods of the first
embodiment, determining the updated position for the feature may
use the relative shift and/or the projection system induced error
determined in the methods described in relation to the second
embodiment.
[0106] In a regular second-to-first layer overlay measurement there
is a bottom grating which is printed during the first layer
exposure, and there is a top grating which is printed during the
second layer exposure. In the second embodiment described above,
the first mark and the second mark are provided on one layer. The
one layer may be the first layer. This means that the relative
responses of different pattern structures due to projection system
heating can be measured after they are printed (i.e. exposed).
[0107] In the second embodiment, there is provided a further method
for controlling positioning of a substrate. The further method may
have all of the same features as described in the second embodiment
and comprises providing a substrate with a first mark on a first
layer and a second mark on a second layer of the substrate. In the
further method, the second mark is the equivalent of the first mark
and the second mark described above. Thus, in the further method,
the second mark comprises at least two types of feature. Thus, the
second mark comprises at least one first portion and at least one
second portion as described above. In the further method, the at
least one first portion corresponds to the first mark described
above and the at least one second portion corresponds to the second
mark described above, and the first mark of the further method
corresponds to an additional mark (i.e. the third mark in the
context of the method already described). The further method may
further comprise determining the position of the first mark and
determining a relative shift of the at least one first portion with
respect to the at least one second portion. The method comprises
controlling positioning of the first layer or a further layer of
the substrate or any layer on a further substrate based on the
determined position and a determined relative shift. The further
method differs from the previously described method due to the
inclusion of the first mark (which corresponds to the third mark in
the method described above). Furthermore, there may be different
numbers of first mark and second mark in the further method.
[0108] Using this further method, the positioning of the first
layer or a further layer of the substrate or any layer on a further
substrate can be controlled based on the position of the first mark
and the relative shift of the at least one first portion with
respect to the at least one second portion. The relative shift of
the at least one first portion with respect to the at least one
second portion can be described as a characteristic of the second
mark. Similarly to the method described above, the relative shift
of the at least one first portion with respect to the at least one
second portion can be used to determine a projection system induced
error and the projection system induced error can be used to
control positioning of the first layer or a further layer of the
substrate or any layer on a further substrate. The relative shift
of the at least one first portion with respect to the at least one
second portion can be determined in the same way as described above
with respect to the first mark and the second mark above, i.e.
using position measurements and/or diffraction based
measurements.
[0109] In the second embodiment, a substrate is provided with the
first mark and the second mark on the relevant layers. For example
the first mark is provided to a first layer and the second marker
is provided to a second layer on the substrate. However, the method
may further comprise a step of exposing the first mark and/or the
second mark on the respective layers of the substrate. This step is
not necessary within the context of one or more embodiments of the
invention because a substrate already comprising these marks can be
provided but the first mark and/or the second mark can be made on
the relevant layers of the substrate using the lithographic tool
100 described above.
[0110] The present embodiment described in the above method and
further method provides many advantages. For example, using the
projection system induced error as described above may reduce
overlay error and thus improve yield of the lithographic process.
As described, static or dynamic offsets between a substrate
alignment mark and product cell may be reduced or removed. As
described, using the method of the second embodiment, the
determined marker position may be corrected by the determined
relative shift (which is based on measurements purely in resist; eg
before processing takes place). As previously mentioned, etching
and other processing may degrade the printed marker. Thus, no mark
asymmetry is expected and measurement before such processing steps
may be more accurate. Therefore the accuracy and precision may be
higher than measuring etched mark with mark asymmetry. The methods
of the second embodiment will improve the correction which can be
applied for each substrate for a known drift using substrate level
control. This means that the correction (for the projection system
induced error) may be substrate specific; eg a relative shift may
be measured for substrate A and a correction may be determined and
applied specifically for a next layer on the same substrate A;
hence corrections are finer than just lot based corrections which
typically apply to 25 substrates at once.
[0111] The present embodiment relaxes the substrate alignment mark
design rules to optimize aberration sensitivity. Thus, it is not
necessary to use expensive experimental determination of
sensitivities for mark design because this can be avoided.
Additionally, there is more freedom to choose active alignment
marks because the projection system induced error can be accounted
for, thus, there is no need (or a reduced need) to consider
aberration sensitivity when selecting an alignment mark.
Furthermore, no additional (e.g. alignment) marker measurements are
needed in order to correct for projection system induced errors.
The first mark and the second mark can be measured prior to the top
layer exposure, e.g. just after resist development (this is bottom
layer exposure) and thus the relative shift can be determined.
During the top layer exposure, there may be additional substrate
alignment measurements (only standard substrate alignment). Thus,
the stored relative shift can be fed back per wafer to the top
layer exposure. Hence there is no throughput impact during the
exposure and also the relative shift is collected at the top layer
exposure.
[0112] In an embodiment, a system is provided comprising a
processor configured to determine a position of a feature
referenced to a substrate and/or control positioning of a
substrate. The processor is configured to carry out the method
according to any one of the embodiments above. The processor may be
part of, or connected to, either the automated process control
(APC) system and/or the supervisory control system.
[0113] The processor may be configured to: measure a position of
the feature, wherein the feature is configured to enable
positioning of the substrate; receive an intended placement of the
feature; determine an estimate of a placement error, wherein the
placement error is the difference between the intended placement
and an actual placement of the feature, based on knowledge of a
relative position of a first feature referenced to a first layer
with respect to a second feature referenced to a second layer,
wherein the first layer and the second layer are on a substrate;
and determine an updated position for the feature using the
estimate of the placement error and the measured position of the
feature.
[0114] The processor may be configured to determine a relative
shift of a first mark with respect to a second mark, wherein the
first mark and the second mark are on one layer of a substrate,
wherein the first mark is different from the second mark; and
control positioning of a further layer of the substrate or a layer
of a further substrate based on the relative shift.
[0115] The processor may be configured to provide a substrate with
a first mark on a first layer and a second mark on a second layer
of the substrate, the second mark comprising at least one first
portion and at least one second portion; determine the position of
the first mark; determine a relative shift of the at least one
first portion with respect to the at least one second portion; and
use the determined position and determined relative shift to
control positioning of the first layer or a further layer of the
substrate or any layer on a further substrate.
[0116] The above methods may be implemented using a computer
program containing one or more sequences of machine-readable
instructions describing methods of combining process model values
and measurement values as described above. There may also be
provided a data storage medium (e.g., semiconductor memory,
magnetic or optical disk) having such a computer program stored
therein.
[0117] In an embodiment, a program is provided for controlling
determining a position of a feature referenced to a substrate
and/or controlling positioning of a substrate. The program may
comprise instructions for carrying out the steps of any of the
methods described above.
[0118] The program may comprise instructions for carrying out the
steps of: measuring a position of the feature, wherein the feature
is configured to enable positioning of the substrate; receiving an
intended placement of the feature; determining an estimate of a
placement error, wherein the placement error is the difference
between the intended placement and an actual placement of the
feature, based on knowledge of a relative position of a first
feature referenced to a first layer with respect to a second
feature referenced to a second layer, wherein the first layer and
the second layer are on a substrate; and determining an updated
position for the feature using the estimate of the placement error
and the measured position of the feature.
[0119] The program may comprise instructions for carrying out the
steps of: determining a relative shift of a first mark with respect
to a second mark, wherein the first mark and the second mark are on
one layer of a substrate, wherein the first mark is different from
the second mark; and controlling positioning of a further layer of
the substrate or a layer of a further substrate based on the
relative shift.
[0120] The program may comprise instructions for carrying out the
steps of: providing a substrate with a first mark on a first layer
and a second mark on a second layer of the substrate, the second
mark comprising at least one first portion and at least one second
portion; determining the position of the first mark; determining a
relative shift of the at least one first portion with respect to
the at least one second portion; and using the determined position
and determined relative shift to control positioning of the first
layer or a further layer of the substrate or any layer on a further
substrate. The computer program may be executed for example within
the control unit LACU of FIG. 1, or some other controller, for
example within a metrology system that includes the metrology
apparatus 140, or in an advanced process control system or separate
advisory tool. The program may optionally be stored in a memory
which is part of or can be accessed by the automated process
control (APC) system and/or the supervisory control system.
[0121] Further embodiments of the invention are disclosed in the
list of numbered embodiments below:
1. A method for determining a position of a feature referenced to a
substrate, the method comprising:
[0122] measuring a position of the feature, wherein the feature is
configured to enable positioning of the substrate;
[0123] receiving an intended placement of the feature;
[0124] determining an estimate of a placement error, wherein the
placement error is the difference between the intended placement
and an actual placement of the feature, based on knowledge of a
relative position of a first reference feature referenced to a
first layer with respect to a second reference feature referenced
to a second layer, wherein the first layer and the second layer are
on a substrate; and determining an updated position for the feature
using the estimate of the placement error and the measured position
of the feature.
2. The method of embodiment 1, further comprising positioning a
substrate on the basis of the updated position of the feature. 3.
The method of embodiment 2 further comprising a step of exposing
the substrate to a radiation beam. 4. The method of embodiment 2 or
3, wherein the method is carried out using a lithographic
apparatus. 5. The method of any of the preceding embodiments,
wherein the feature is on the first layer or on the second layer.
6. The method of any of the preceding embodiments, wherein the
feature is on a layer of a substrate having the first layer and the
second layer, and the feature is on a different layer than the
first layer and the second layer. 7. The method of any of the
preceding embodiments, wherein the position of the feature is
measured on a substrate different from the substrate associated
with the determined estimate of the placement error. 8. The method
of any of the preceding embodiments, wherein the method further
comprises measuring the position of a first reference feature
relative to the position of a second reference feature to determine
an overlay error and using the overlay error to determine the
estimate of the placement error. 9. The method of any of the
preceding embodiments, wherein the method further comprises
modelling an overlay error between the first layer and the second
layer to determine the position of the first reference feature
relative to the position of the second reference feature. 10. The
method of embodiment 9, further comprising receiving context
information and/or lithographic apparatus information, and using
the context information and/or lithographic apparatus information
to model the overlay error, wherein the context information and/or
lithographic apparatus relates to measured and/or modelled
deformation of at least one of the substrate, a patterning device
and/or a projection system. 11. The method of embodiment 9 or 10,
wherein modelling the overlay error comprises using a predetermined
value based on overlay data. 12. The method of any one of
embodiments 8 to 11, wherein the estimate of the placement error is
determined to be the same as the overlay error. 13. The method of
any one of the preceding embodiments, wherein the feature is a
grating and/or an alignment mark. 14. A system comprising a
processor configured to determine a position of a feature
referenced to a substrate, the processor being configured to:
[0125] measure a position of the feature, wherein the feature is
configured to enable positioning of the substrate;
[0126] receive an intended placement of the feature;
[0127] determine an estimate of a placement error, wherein the
placement error is the difference between the intended placement
and an actual placement of the feature, based on knowledge of a
relative position of a first reference feature referenced to a
first layer with respect to a second reference feature referenced
to a second layer, wherein the first layer and the second layer are
on a substrate; and
[0128] determine an updated position for the feature using the
estimate of the placement error and the measured position of the
feature.
15. A program for controlling determining a position of a feature
referenced to a substrate, the program comprising instructions for
carrying out the steps of:
[0129] measuring a position of the feature, wherein the feature is
configured to enable positioning of the substrate;
[0130] receiving an intended placement of the feature;
[0131] determining an estimate of a placement error, wherein the
placement error is the difference between the intended placement
and an actual placement of the feature, based on knowledge of a
relative position of a first reference feature referenced to a
first layer with respect to a second reference feature referenced
to a second layer, wherein the first layer and the second layer are
on a substrate; and determining an updated position for the feature
using the estimate of the placement error and the measured position
of the feature.
16. A method for controlling positioning of a substrate,
comprising:
[0132] providing a substrate with a first mark and a second mark on
one layer of the substrate, wherein the first mark is different
from the second mark;
[0133] determining a relative shift of the first mark with respect
to the second mark; and
[0134] controlling positioning of the one layer of the substrate, a
further layer of the substrate or a layer of a further substrate
based on the determined relative shift.
17. The method of embodiment 16, wherein the first mark and the
second mark have different sensitivities to an aberration in a
projection system, wherein the projection system is used to expose
the first mark and the second mark on the substrate. 18. The method
of embodiment 16 or 17, further comprising determining a projection
system induced error using the determined relative shift and the
controlling positioning of the one layer of the substrate, a
further layer of the substrate or a layer of a further substrate
uses the determined projection system induced error. 19. The method
of any one of embodiments 16-18, further comprising measuring the
position of the first mark and the second mark and calculating the
distance between the first mark and the second mark, and wherein
the relative shift is determined using the calculated distance
between the first mark and the second mark and an expected distance
between the first mark and the second mark. 20. The method of any
one of embodiment 16-18, wherein the relative shift is determined
using a diffraction based measurement. 21. The method of any one of
embodiments 16-20, wherein the determined relative shift is used in
a feedback loop to control positioning of a layer of a further
substrate and/or in a feedforward loop to control positioning of a
further layer of the same substrate. 22. The method of any one of
embodiments 16-21, wherein the first mark is an alignment mark or
an overlay mark, and wherein the second mark is a product feature
or a feature having a similar response to the projection system
induced error as a product feature. 23. The method of any one of
embodiments 16-22, wherein the layer comprising the first mark
comprises at least five to ten first marks and the layer comprising
the second mark comprises the same number of second marks. 24. The
method of any one of embodiments 16-23, wherein the first mark and
the second mark overlap. 25. The method of any one of embodiments
16-24, wherein the first mark has multiple first portions and the
second mark has multiple second portions. 26. A method for
controlling positioning of a substrate, comprising:
[0135] providing a substrate with a first mark on a first layer and
a second mark on a second layer of the substrate, the second mark
comprising at least one first portion and at least one second
portion;
[0136] determining the position of the first mark;
[0137] determining a relative shift of the at least one first
portion with respect to the at least one second portion; and
[0138] controlling positioning of the first layer or a further
layer of the substrate or any layer on a further substrate based on
the determined position and the determined relative shift.
27. The method of embodiment 26, wherein the at least one first
portion and the at least one second portion have different
sensitivities to an aberration in a projection system, wherein the
projection system is used to expose the second mark. 28. The method
of embodiment 26 or 27, wherein the relative shift is determined by
measuring of a position of the at least one first portion and a
position of the at least one second portion and/or using a
diffraction based measurement. 29. The method of any one of
embodiments 26-28, wherein the first mark has multiple first
portions and the second mark has multiple second portions. 30. The
method of any one of embodiments 29, wherein the first portions and
the second portions are interlaced. 31. The method of any one of
embodiments 26 to 30, wherein a first portion comprises fewer
elements than a second portion. 32. The method of any one of
embodiments 26-31, wherein a first portion comprises only a single
element. 33. The method of any one of embodiments 26-32, wherein a
single element of a first portion is larger than a single element
of a second portion. 34. The method of any one of embodiments
26-33, wherein at least one of the second portions comprises a
plurality of elements. 35. The method of embodiment 34, wherein the
pitch between the second portions is larger than the pitch between
the plurality of elements of the second portion. 36. The method of
embodiment 34 or 35, wherein a single element of a first portion
corresponds in size to the plurality of elements making up a second
portion. 37. The method of any one of embodiments 26 and 29-36,
wherein the first portions are substantially consistent in shape
and pitch, and the second portions are substantially consistent in
shape and pitch. 38. The method of any one of embodiments 26-36,
wherein the determined position and the relative shift are used to
determine a projection system induced error and the projection
system induced error is used to control positioning of the first
layer or a further layer of the substrate or any layer on a further
substrate. 39. The method of any one of embodiments 18-25 or 38,
wherein the determined projection system induced error is due to
projection system drift and/or projection system heating. 40. The
method of any one of embodiments 18-25, 38 or 39, wherein the
determined projection system induced error is used in a feedback
loop to control positioning of a layer of a further substrate
and/or in a feedforward loop to control positioning of a further
layer of the same substrate. 41. The method of any one of
embodiments 16-40, further comprising exposing the first mark and
the second mark on the respective layer of the substrate. 42. The
method of any one of embodiments 1 to 13, wherein determining the
updated position for the feature uses the relative shift and/or the
projection system induced error determined in any one of
embodiments 16 to 41. 43. A system comprising a processor
configured to control positioning of a substrate, the processor
being configured to:
[0139] determine a relative shift of a first mark with respect to a
second mark, wherein the first mark and the second mark are on one
layer of a substrate, wherein the first mark is different from the
second mark; and control positioning of a further layer of the
substrate or a layer of a further substrate using the determined
relative shift.
44. A program for controlling positioning of a substrate, the
program comprising instructions for carrying out the steps of:
[0140] determining a relative shift of a first mark with respect to
a second mark, wherein the first mark and the second mark are on
one layer of a substrate, wherein the first mark is different from
the second mark; and controlling positioning of a further layer of
the substrate or a layer of a further substrate using the
determined relative shift.
45. A system comprising a processor configured to control
positioning of a substrate, the processor being configured to:
[0141] provide a substrate with a first mark on a first layer and a
second mark on a second layer of the substrate, the second mark
comprising at least one first portion and at least one second
portion;
[0142] determine the position of the first mark;
[0143] determine a relative shift of the at least one first portion
with respect to the at least one second portion; and
[0144] use the determined position and the determined relative
shift to control positioning of the first layer or a further layer
of the substrate or any layer on a further substrate.
46. A program for controlling positioning of a substrate, the
program comprising instructions for carrying out the steps of:
[0145] providing a substrate with a first mark on a first layer and
a second mark on a second layer of the substrate, the second mark
comprising at least one first portion and at least one second
portion;
[0146] determining the position of the first mark;
[0147] determining a relative shift of the at least one first
portion with respect to the at least one second portion; and
[0148] using the determined position and the determined relative
shift to control positioning of the first layer or a further layer
of the substrate or any layer on a further substrate.
CONCLUSION
[0149] In conclusion, the present disclosure provides a method
generating an updated position for a feature referenced to a
substrate, which can be used in various different ways. This allows
the error introduced when forming the feature to be reduced or
negated by processing steps. The present disclosure also provides a
method for controlling positioning of a substrate. This allows the
effect of projection system induced error to be reduced or
prevented.
[0150] The disclosed methods allow the provision of a lithographic
apparatus and methods of operating a lithographic apparatus in
which performance parameters such as overlay can be improved,
without the need for additional measurements, or even with a
reduced number of measurements. The determination of the first
reference feature and the second reference feature can be performed
with or without using additional context information and/or
lithographic apparatus information. Throughput can be maintained
and/or increased, due to the increased accuracy which substrates
(including those for which no measurement data associated with the
first reference feature and the second reference feature is
available) can be positioned without the loss of performance that
might otherwise result.
[0151] The steps of combining determining an estimate of the
placement error and determining an updated position can be
performed in any suitable processing apparatus, which may located
anywhere in the facility of FIG. 1, or may be physically remote
from the facility. Steps of the method may be carried out in
separate parts of the apparatus.
[0152] The updated position and/or estimated position error may be
calculated in the supervisory control system of FIG. 1, or in the
litho tool control unit LACU. They may be calculated in a remote
system and communicated to the facility afterwards. Any model and
measurement data may be delivered separately to a processing
apparatus which then combines them as part of calculating the
estimate of the position error and/or the updated position.
[0153] The method and variations above are described as being
carried out using a lithographic apparatus. However, other
apparatus may be used. The patterning step of a lithographic
manufacturing process is only one example where the principles of
the present disclosure may be applied. Other parts of the
lithographic process, and other types of manufacturing process, may
also benefit from the generation of modified estimates and
corrections in the manner disclosed herein.
[0154] These and other modifications and variations can be
envisaged by the skilled reader from a consideration of the present
disclosure. The breadth and scope of the present invention should
not be limited by any of the above-described exemplary embodiments,
but should be defined only in accordance with the following claims
and their equivalents.
* * * * *